1. Field of the Invention
The present invention relates to a semiconductor light emitting array device. More particularly, the invention relates to the semiconductor light emitting array device in which the light emitting area is divided to a plurality of light emitting segments by separating grooves.
2. Description of the Related Art
The semiconductor light emitting array devices have been developed for the purpose of application to a light source of a printer or a copying apparatus using ordinary papers. One of such array devices is a surface light emitting type diode array in which a number of square light emitting segments are disposed along a predetermined line in a plane parallel to the substrate surface. Another array device is a side end light emitting type diode array in which a plurality of optical outputs arranged along a predetermined line are obtained from a side end surface perpendicular to the substrate surface.
An essential structure of the surface light emitting type diode array is disclosed, for example, in a prepublication text 1-211 for all Japan Electronic and Communication Society Symposium Meeting, Communication Branch, 1980. In accordance with the general surface light emitting type diode array, electrodes are formed at the both ends of or around each of the light emitting elements so as to even the optical intensity from the elements throughout the whole area of the light emitting portion of the diode array. Therefore, the electrodes and the light emitting elements are formed on the same plane so that each light emitting segment requires a space for the electrode and the light emitting element plus the element separating area. In accordance with such a structure, it is very difficult to form the light emitting elements in a high density, for example, more than 600 dpi (dots per inch).
Besides, in accordance with such a structure, a large gap is formed between the near field patterns of the light emitting elements. That is, the near field patterns are not continuous in the direction of the horizontal scanning (main scanning) along the row of the light emitting elements. Therefore, though it is possible to continuously scan in the direction of the vertical scanning (subscanning), it is impossible to completely scan along a line in the horizontal scanning direction. As a result, white stripes are formed in the vertical scanning direction in the printed image, which degrades the quality of the print.
An example of the side end light emitting type diode array is disclosed in Japanese Patent Application Laying Open (KOKAI) No. 60-32373. In the published example, a plurality of light emitting elements are formed side by side in a stacked structure formed on the substrate. The light emitting elements are isolated from each other electrically and spatially by separating grooves each of which extends in the direction perpendicular to the light emitting side end surface. In accordance with such a structure, the light emitting element surface and the electrode surface are not formed in the same plane so that the space required for each light emitting segment is a width of the light emitting element plus the element separating groove. Therefore, it is theoretically possible to arrange the light emitting elements in a high density more than 600 dpi. However, also in this case as in the case of the surface light emitting type diode array, mentioned above, a large gap is formed between the adjacent two near field patterns of the light emitting elements since the separating groove is formed along the direction perpendicular to the light emitting side end surface, i.e., parallel to the light emitting direction in a plane parallel to the substrate surface. Therefore, the near field patterns are discontinuous along the direction of light emitting elements row, which impedes the complete line scanning in the horizontal scanning direction, as in the case of the surface light emitting type diode array. Accordingly, the white stripes are still formed in the printed image so that the print quality of the side end light emitting type diode array is still insufficient.
In the above-mentioned side end light emitting type diode array, it has been considered to minimize the width of the element separating groove for the purpose of deletion or minimizing the white stripes generated in the printed image along the vertical scanning direction. The groove is formed from the layer-stacked structure surface through the active layer of the light emitting area to the substrate. The light emitting area is formed 2 to 50 .mu.m deep from the surface of the layer-stacked structure according to the light emission efficiency. Therefore, if the groove to be formed as narrow as 1 to 2 .mu.m wide to avoid the degradation of the print quality, the aspect ratio (depth/width) of the groove section becomes up to 1 to 50. It is technically very difficult to accurately form such a groove having a large aspect ratio. Besides, even if it becomes possible to form such a narrow groove in the stacked structure, it is still impossible to completely delete the white stripes along the vertical scanning direction in the printed image since the groove is still exists, even if very thin, between the light emitting elements, which forms the gap between the adjacent near field patterns of the light emitting elements.
For the reasons mentioned above, it has not been achieved to realize a semiconductor light emitting array device for a printing apparatus which makes it possible to obtain a print image of high density and high quality.